The present disclosure relates to a recording device performing at least recording on an optical recording medium including a reference face on which information recording including radial positional information is performed in a CAV (Constant Angular Velocity) manner, and a recording layer formed at a depth position different from the reference face, and a method thereof.
As an optical recording medium for the recording and reproducing of signals through the irradiation of light, so-called optical discs such as CDs (Compact Discs), DVDs (Digital Versatile Discs), and BDs (Blu-ray Discs: Registered Trademark) have come into use.
Concerning an optical recording medium taking a major role in the next generation of the optical mediums relating to the currently widespread CD, DVD, and BD, and the like, the applicant proposes a so-called bulk recording type (merely, also referred to as a bulk type) optical recording medium described in Japanese Unexamined Patent Application Publication Nos. 2008-135144 and 2008-176902.
For example, as shown in FIG. 21, bulk recording is for performing multilayer recording in a bulk layer 102 by performing laser beam irradiation while sequentially changing the infocus position, which is a technique for achieving high capacity recording, and relates to an optical recording medium (a bulk type recording medium 100) having at least a cover layer 101 and a bulk layer (a recording layer) 102.
Concerning such bulk recording, in Japanese Unexamined Patent Application Publication No. 2008-135144, a recording technique which is a so-called micro-hologram method is disclosed. In the micro-hologram method, a so-called hologram recording material is used as the recording material of the bulk layer 102. As the hologram recording material, a photopolymerization-type photopolymer and the like are widely known.
The micro-hologram method is broadly divided into two methods of a positive type micro-hologram method and a negative type micro-hologram method.
The positive type micro-hologram method is a method of condensing two opposed light fluxes (light flux A and light flux B) at the same position and forming a micro-interference pattern (hologram) to use the interference pattern as a recording mark.
As a concept opposite to the positive type micro-hologram method, the negative type micro-hologram method is a method of erasing a previously formed interference pattern through irradiation of laser light to use the erased portion as a recording mark. In the negative micro-hologram method, a process of forming an interference pattern on a bulk layer in advance is necessary as an initialization process.
As a method of bulk recording different from the micro-hologram method, the applicant also proposes, for example, a recording method of forming a void (vacancy or blank) disclosed in Japanese Unexamined Patent Application Publication No. 2008-176902, as a recording mark.
The void recording method is a method of performing laser irradiation with relatively high power on the bulk layer 102 formed of a recording material such as photopolymerization type photopolymer, to record a void in the bulk layer 102. As described in Japanese Unexamined Patent Application Publication No. 2008-176902, the vacancy portion formed as described above has a refractive index different from that of the other portion in the bulk layer 102, and it is possible to raise the reflectance of light at such a boundary portion. Accordingly, the vacancy portion serves as a recording mark, and thus information recording based on the forming of the vacancy mark is realized.
Since such a void recording method is not for forming the hologram, the irradiation of light from one side may be performed in the recording. That is, it is not necessary to condense two light fluxes at the same position to form the recording mark in the same manner as the positive type micro-hologram method.
In comparison with the negative micro-hologram method, there is merit in that the initialization process may not be necessary.
In Japanese Unexamined Patent Application Publication No. 2008-176902, an example of performing irradiation of pre-cured light before recording when performing the void recording is described. However, even when the irradiation of such pre-cured light is omitted, the recording of a void is possible.
Although it is a bulk recording type (simply referred to as bulk type) optical recording medium for which various recording methods are proposed as described above, the recording layer (bulk layer) of such a bulk type optical recording medium does not have an evincive multilayer structure, for example, meaning one in which a plurality of reflection films are formed. That is, in the bulk layer 102, a reflection film and a guiding groove for each recording layer, which is provided in a general multilayer disc, are not provided.
Accordingly, in the state of the structure of the bulk type recording medium 100 itself shown in FIG. 21, focus servo or tracking servo may not be performed at the time of recording in which the mark is not formed.
For this reason, in practice, the bulk type recording medium 100 is provided with a referential reflection face (reference face) having guiding grooves as shown in FIG. 22.
Specifically, guiding grooves (position guides) are formed in a spiral shape or concentric shape, for example, by forming pits or grooves on the lower face side of the cover layer 101, and a selective reflection film 103 is formed thereon. On the lower layer side of the cover layer 102 on which the selective reflection film 103 is formed as described above, a bulk layer 102 is laminated as an intermediate layer 104 in the drawing through an adhesive material such as UV curable resin.
By forming the guiding grooves using the pits or grooves as described above, absolute positional information (address information) such as radial positional information and rotation angle information is recorded. In the following description, a face on which such guiding grooves are formed and the absolute positional information is recorded (in this case, the forming face of the selective reflection film 103) is called “reference face Ref”.
After forming the medium structure as described above, in the bulk type recording medium 100, as shown in FIG. 23, servo laser light (merely referred to as servo light) as laser light for positional control is irradiated, separately from laser light (hereinafter, referred to as recording and reproducing laser light, or merely recording and reproducing light) for recording (or reproducing) a mark.
As shown, the bulk type recording medium 100 is irradiated with the recording and reproducing laser light and the servo laser light through a common object lens.
In this case, if the servo laser light reaches the bulk layer 102, there may be an adverse effect on the mark recording in the bulk layer 102. For this reason, in the bulk recording method of the related art, laser light having a wavelength band different from that of the recording and reproducing laser light is used as the servo laser light, and the selective reflection film 103 having wavelength selectivity in which the servo laser light is reflected and the recording and reproducing laser light passes is provided as a reflection film formed on the reference face Ref.
Under the presupposition of the above-description, an operation at the mark recording time on the bulk type recording medium 100 will be described with reference to FIG. 23.
First, when multilayer recording is performed on the bulk layer 102 on which the guiding groove or the reflection film is not formed, it is predetermined where the layer position for recording the mark in the depth direction in the bulk layer 102. In the drawing, as the layer position (mark forming layer position: also referred to as the information recording layer position) for forming the mark in the bulk layer 102, a case of setting a total of five information recording layer positions L of a first information recording layer position L1 to a fifth information recording layer position L5 is exemplified. As shown, the first information recording layer position L1 is set as a position separated from the selective reflection film 103 (reference face Ref) on which the guiding grooves are formed in a focus direction (depth direction) by a first offset of-L1. The second information recording layer position L2, the third information recording layer position L3, the fourth information recording layer position L4, and the fifth information recording layer position L5 are set as positions separated from the reference face Ref by a second offset of-L2, a third offset of-L3, a fourth offset of-L4, and a fifth offset of-L5, respectively.
During recording when the mark is not formed yet, the focus servo and the tracking servo on each layer position in the bulk layer 102 based on the reflection light of the recording and reproducing laser light may not be performed. Accordingly, focus servo control and tracking servo control of the object lens during recording are performed such that a spot position of the servo laser light follows the guiding grooves with respect to the reference face Ref on the basis of the reflection light of the servo laser light.
However, the recording and reproducing laser light should reach the bulk layer 102 formed further to the lower side than the reference face Ref to record a mark. For this reason, in the optical system in this case, a recording and reproducing light focus mechanism for independently adjusting the infocus position of the recording and reproducing laser light is provided separately from the focus mechanism of the object lens.
Specifically, such a focus mechanism is provided with an expander changing collimation of recording and reproducing laser light input to the object lens. That is, by changing the collimation of the recording and reproducing laser light input to the object lens, the infocus position of the recording and reproducing laser light can be adjusted independently from the servo laser light.
By providing the focus mechanism for such a recording and reproducing laser light, the infocus position of the recording and reproducing laser light can be adjusted at a necessary information recording layer position L in the bulk layer 102 and can be controlled at a position just under a guiding groove formed on the reference face Ref, by performing the focus control of the object lens and the tracking servo control on the basis of the reflection light of the servo laser light from the reference face Ref.
When the recording is performed on the bulk type recording medium 100 on which the mark recording has already been performed, in the same manner as during recording it is not necessary to control the position of the object lens on the basis of the reflection light of the servo laser light. That is, during reproducing, the focusing of the object lens and the tracking servo control may be performed on the mark rows formed at the information recording layer position L (also referred to as an information recording layer L during reproduction) that is the reproduction target on the basis of the reflection light of the recording and reproducing laser light.
An example of the related art is disclosed in Japanese Unexamined Patent Application Publication No. 2001-118245.
As described above, at the time of recording on the bulk type recording medium 100, the mark row is recorded at a desired position in the bulk layer 102 by infocusing the recording and reproducing laser light at the necessary information recording layer position L in the bulk layer 5 while performing the focus servo and the tracking servo on the reference face Ref by the servo laser light.
Information such as absolute value positional information is recorded on the reference face Ref by forming the position guide based on, for example, pit rows (mark rows) or grooves, as described above. However, it is thought that the information recording is performed on the reference face Ref not by a CLV (Constant Linear Velocity) method but by a CAV (Constant Angular Velocity) method.
When the information recording on the reference face Ref is performed by the CAV method as described above, it follows that, the bulk type recording medium 100 is rotated by CAV (rotation at constant velocity). When the bulk type recording medium 100 is rotated by CAV as described above, the mark recording on the bulk layer 102 is also performed by the CAV method.
However, as is commonly known, the recording based on the CAV method causes a decrease in recording density as compared with the recording based on the CLV method. For this reason, it is difficult to avoid a decrease in recording capacity of the bulk layer 102.